1. Field of the Invention
The present invention is installed in an apparatus for feeding paper or the like, and relates to a device for detecting overlapped paper feed.
2. Description of the Related Art
A paper feeding apparatus which is applied to a printer, a copier or the like feeds paper along a feeding path. In the paper feeding apparatus, a device for detecting overlapped feed of paper to be fed is set.
An overlapped feed detecting device has a light transmission type sensor comprising a light emitting element and a light receiving sensor placed face to face along the feeding path so that it can detect overlapped feed of paper based on an output value in response to a state of light transmission.
To detect double feeding of thin or thick paper by using one light transmission type sensor, it is necessary to adjust the light emission from the light emitting element and the amplification ratio of the output from the light receiving sensor (the sensibility of the light receiving sensor) in accordance with the thickness of the paper or the like to be used. FIG. 8 is a diagram showing a configuration of such a conventional overlapped feed detecting device.
The light emission from a light emitting element 40 is manually adjusted by using a manual light emission adjustment circuit 41a. The light is received by a light receiving sensor 42 facing the light emitting element 40, between which paper is fed. The output from the light receiving sensor 42 is input to an amplifying circuit 43, and the amplification ratio is manually adjusted by using a manual amplification ratio adjustment circuit 44a. An output signal amplified at the amplification ratio is A/D-converted by an A/D converter 46 installed in a microcomputer 45 and input to a CPU 47.
The CPU 47 is connected with both a ROM 48 and a RAM 49 and judges overlapped paper feed based on the input signal. When overlapped feed is detected, an overlapped feed warning lamp 50 installed in an operation panel or the like flashes and processing used in unusual situation, such as suspension of paper feed, is carried out.
In the above configuration, the light emission from the light emitting element 40 and the amplification ratio of the amplifying circuit 43 are increased for thick paper which has low light transmissivity, while decreased for thin paper which has high light transmissivity. A user needs to carry out this adjustment by using the manual light emission adjustment circuit 41a or the manual amplification ratio adjustment circuit 44a, which is time consuming and may cause erroneous setting.
To solve the inconvenience associated with the manual setting, there has been another method which automatically adjusts the light emission from the light emitting element 40 or the amplification ratio for amplifying the output from the light receiving sensor 42 in response to the thickness of paper to be used. FIG. 9 is a diagram showing a configuration of such an overlapped feed detecting device.
In this device, the CPU 47 changes the light emission from the light emitting element 40 and the amplification ratio of the amplifying circuit 43 in order to make the output signal from the light receiving sensor 42 appropriate for overlapped feed detection. In other words, the CPU 47 automatically adjusts a light emission adjustment circuit 41b or an amplification ratio adjustment circuit 44b.
However, in this method, an algorithm for adjustment is complicated, which makes a program for automatic adjustment processing complex. Furthermore, since repeated adjustment and judgment is necessary, it is time consuming to adjust optimally.